N = int(input())
K = int(input())
dp = [[[0 for _ in range(6*N+1)] for _ in range(6*N+1)] for _ in range(N+1)]
dp[0][0][0] = 1
for i in range(1,N+1):
    for j in range(6*N+1):
        for k in range(6*N+1):
            if i<=N-K:
                for j1 in range(1,min(6,j)+1):
                    for k1 in range(1,min(6,k)+1):
                        dp[i][j][k] += dp[i-1][j-j1][k-k1]
            else:
                for j1 in range(4,min(6,j)+1):
                    for k1 in range(1,min(6,k)+1):
                        dp[i][j][k] += 2*dp[i-1][j-j1][k-k1]
ans = 0
for k in range(1,6*N):
    for j in range(k+1,6*N+1):
        ans += dp[N][j][k]
print(ans/(pow(6,N)**2))